Introduction

The Arena is the place where you fight random players in the quest for reputation and shinies.
Each day you get a certain number of fights in the Arena which you use to battle against other ninjas.
There are no requirements to fight in the Arena. You are randomly matched up with an opponent with the greatest odds of them being at or near your level/season. Sometimes though, you get unlucky and fight someone significantly stronger.
An arena fight is similar to a mission with a difficulty around 6-9. Both players "roll", and the player with most successes wins the fight. In the event of a tie, the attacking character, (you), will always win. The battle stat is randomly chosen from Genjutsu, Ninjutsu and Taijutsu.
For each fight you do, you get Arena Reputation. You get 30 Rep for a win, and much less Rep when you lose.

Your Shadow

Odds are that you'll get an opponent at or near your Level and Season. This includes yourself. If you draw yourself as your opponent, you'll fight Your Shadow. The fewer characters that are close to you in Levels and Season, the greater the chances of fighting Your Shadow are. Your Shadow is you, exactly, with the same Items and Stats as you. Therefore, assuming you have enough Strength to meet the Difficulty of the Arena Battle, you and Your Shadow will have the same number of Levels + Successes, and so will result in a tie, and thus your victory. Beating Your Shadow gets you a special Prize and a Trophy1.

Fights

When you start as a new player you get 2 daily fights. There are items, upgrades, and other things which increase the number of fights. You can also use Ryo to buy 3 additional fights, but the cost increases by a multiple of 4 every time you use this option. This cost increase resets at dayroll. There are also potions which helps you out.

Ryo cost

Dark Hour

The Dark Hour appears four times a day-two times AM and two times PM, and lasts for an hour. These hours are chosen randomly each dayroll and can be viewed on the main menu.
During this period players who have gained the permanent item Dark Band can fight each other to increase their Moon state, although players without this item are still free to fight during dark hour. A Dark Hour battle has a slightly higher difficulty than a normal battle.